In recent years, there has been a growing need to integrate industrial control systems across a plurality of different types of networks and protocols while maintaining communications performance of smaller or more-proprietary systems. One problem here is that often times a desired communication interface and required communications services do not match. For code compatibility, it may be desirable to use an existing industrial protocol interface, yet there is a need for higher level services, such as gateway functions, multicast or time synchronization, which generally are not available. In many cases, either the communication service interface need to be changed to a more full featured protocol or the existing protocol need be enhanced to support the required features.
Along with communicating on a desired network, consider the situation where a PLC desires to implement connectivity via an industrial network protocol. Newer protocols such as EtherNet/IP have a rich set of application-level objects as well as complex network protocol layers. A PLC implementing EtherNet/IP connectivity will find it useful to include application layer features (application objects). However, it is desirable not to require the PLC processor to implement the entire EtherNet/IP network layer. There are several current methods in which industrial protocol support is implemented in PLCs. Existing EtherNet/IP implementations, for example, generally implement the network and application layers in the PLC itself, using the backplane between the PLC and Network Interface Module as a network hop. For older and simpler protocols, PLCs often use a dual-port or memory-map interface between the PLC and Network Interface Module to transport the actual industrial protocol packets.